Fix the Builder launcher's broken layout and unstyled controls

[dovvnloading]

Problem

The Builder dialog's form rendered as a single inline run: the Recipe label, its <select>, and the goal label all shared one line before the full-width <textarea> wrapped, and the panel stretched toward its 880px max as a result.

Root cause: <Dialog>'s className lands on the panel (.overlay-dialog), never on the body. So .builder-launch-dialog { display: flex; flex-direction: column } only ever spaced the header away from the body, while .overlay-dialog-body stayed a plain block full of inline-level children.

Separately, the three budget inputs had no styling beyond width: 110px, so they rendered as default-white browser fields inside a dark dialog; the fieldsets and radios were likewise raw browser defaults.

Change

• Scoped the form layout to .overlay-dialog-body, the way .settings-dialog / .help-dialog / .library-dialog already do, and pinned the dialog to 540px.
• All three control kinds (select, textarea, number) now share one themed box matching .settings-select's existing treatment; fieldsets match .settings-fieldset; radios get accent-color.
• Oversight radios are now whole-row targets with a title and description rather than one flat sentence, and the chosen row is visibly marked.
• The autopilot disclosure is a bordered callout instead of loose orange text — it is a real "this will act without asking" warning.
• listRecipes has always returned each recipe's description and nothing ever rendered it, so the picker gave no clue what a recipe builds. The selected recipe's description now shows under the picker.
• The start button spent its whole default state disabled while looking identical to enabled — it now dims.

No behavior change to builder/start: the same args, in the same order, with the same enable/disable rule.

Test plan

• BuilderLaunchDialog.test.tsx — 8 passed, including two new tests (selected-row marking; recipe description rendering). The 6 pre-existing tests were not modified.
• Full frontend suite: 1845 passed across 77 files.
• npx tsc --noEmit -p . — clean.
• npx eslint . — 0 errors.
• Verified in a live browser against the real backend via DOM geometry: the dialog body computes flex/column, the four fields sit at distinct offsets each at full width (previously three shared one row), and the number inputs compute rgb(32,32,32) with light text instead of default white.

Note: the selected-row highlight could not be confirmed visually — the browser pane runs hidden here and does not recompute styles for dynamically toggled classes, so that state is covered by the new test instead.